Method for reducing tapping temperature of converter

Abstract

The invention relates to the technical field of iron and steel smelting, and discloses a method for reducing the tapping temperature of a converter, which comprises the following steps: (1) the converter tapping method adopts a direct tapping method without turning down a converter when a gun is lifted; (2) long nozzle and argon blowing protection casting is adopted for large ladle casting in the continuous casting process; (3) controlling the temperature of the alloy added in the converter tapping process to be greater than or equal to 300 DEG C; and (4) steel ladle baking is conducted according to a refractory heating curve, the baking time is smaller than or equal to 15-25 h, and the steel ladle online final temperature is controlled to be larger than or equal to 1000 DEG C. By reducing the tapping temperature of the converter, the effects of improving the quality of molten steel, prolonging the service life of the converter and reducing the production cost can be achieved.

Description

Technical Field

[0001] The present invention relates to a method for reducing the steel tapping temperature of a converter. Background Art

[0002] In the field of iron and steel metallurgy, molten steel temperature is a very important process parameter throughout the steelmaking and continuous casting process. Appropriate molten steel temperature is an important prerequisite for ensuring the smooth production of steelmaking and continuous casting and the quality of steel products. For steel mills, the symbol of the converter production level is the converter tapping temperature. Whether the tapping temperature is reasonable directly affects the output and the consumption of steel, alloy, refractory and other economic and technical indicators. Reasonably lowering the molten steel temperature is a key technical issue for the metallurgical industry to improve the level of steelmaking technology and is one of the main production technical indicators. Therefore, controlling the converter tapping temperature is of great significance to the completion of various indicators.

[0003] Excessively high tapping temperature of the converter can cause the following hazards:

[0004] (1) The converter end temperature is proportional to the oxygen content in the steel. The higher the converter end temperature, the more oxygen content in the steel, the more deoxidizer is used, the lower the alloy yield is, the more deoxidation products are, the more inclusions in the steel are, and the quality of the molten steel is affected.

[0005] (2) Excessively high tapping temperature will seriously corrode the magnesia carbon bricks in the working layer of the converter, reduce the life of the converter and the ladle, increase the consumption of refractory materials per ton of steel, and cause refractory inclusions to flow into the molten steel, seriously affecting the quality of the molten steel.

[0006] (3) Excessively high tapping temperature will increase the probability of serious accidents such as large-package steel leakage and steel leakage during pouring. Summary of the invention

[0007] In view of this, the present invention provides a method for reducing the steel tapping temperature of a converter. By reducing the steel tapping temperature of the converter, the effects of improving the quality of molten steel, extending the service life of the converter and reducing production costs can be achieved.

[0008] In order to solve the above technical problems, the present invention provides a technical solution: a method for reducing the steel tapping temperature of a converter, which comprises the following steps:

[0009] (1) The converter steel-tapping method adopts the converter steel-tapping method without turning over the converter: after the oxygen lance is lifted at the end of converter blowing, the depth of the oxygen lance tip entering the furnace mouth is determined according to the difference between the absolute height of the oxygen lance and the absolute height of the furnace mouth, the oxygen lance tip is inserted into the furnace mouth, the nitrogen shut-off valve is opened, and nitrogen is continuously blown. The nitrogen blowing time is determined according to the slag splashing out of the furnace mouth;

[0010] (2) In the continuous casting process, long shroud and argon blowing protection casting are used for ladle casting;

[0011] (3) Control the temperature of the alloy added during the converter steelmaking process to be ≥300°C;

[0012] (4) The ladle is baked according to the refractory temperature rise curve, the baking time is ≤15-25h, and the ladle end temperature is controlled to be ≥1000℃.

[0013] Furthermore, in step (1), the oxygen lance tip enters the furnace mouth at a depth of 1 to 1.5 m.

[0014] Furthermore, in step (1), the blowing time of nitrogen is 10-30 seconds. More preferably, after the nitrogen blowing starts, if a large number of dense slag pieces appear at the furnace mouth, the blowing time is controlled according to the upper limit of 30 seconds; if only a small amount of slag pieces splash at the furnace mouth, the blowing time is controlled according to the lower limit of 10 seconds.

[0015] Furthermore, in step (2), the argon blowing flow rate of the long shroud is controlled to be above 55 L / min. The argon blowing flow rate of the long shroud is controlled to be above 55 L / min to improve the protective casting effect and prevent the secondary oxidation of the molten steel when it is poured from the ladle (steel ladle) into the tundish, thereby generating a large amount of Al2O3 inclusions.

[0016] Furthermore, in the step (3), an alloy baking device is used to bake and heat the alloy, the fuel gas medium used by the alloy baking device is converter gas, and the combustion mode is oxygen-enriched combustion.

[0017] Furthermore, in step (4), the ladle baking is performed by using a ladle baking machine, and the fuel gas medium used by the ladle baking machine is blast furnace gas, oxygen and converter gas.

[0018] Furthermore, the diameter of the pipeline connecting the converter gas to the gas inlet of the ladle roaster is 200 mm, and the diameter of the pipeline connecting the blast furnace gas to the gas inlet of the ladle roaster is 800 mm.

[0019] Furthermore, the ladle cover of the ladle roaster is provided with a preheating box, and the combustion-supporting air is heated by the heat storage body and then collected in two ways to the burner, thereby improving the thermal efficiency of roasting.

[0020] The principle of reducing the steel tapping temperature of the present invention is:

[0021] (1) The end point composition needs to be detected during the converter smelting process. Each detection requires sampling and temperature measurement of the molten steel composition in the furnace, which takes about 3 minutes. The present invention can improve the converter turning rate by adopting a method of directly tapping the converter without turning the converter, thereby accelerating the converter smelting rhythm and shortening the converter smelting cycle.

[0022] (2) During the continuous casting process, the ladle casting adopts a long water nozzle and argon blowing protection casting, which can reduce the contact between high-temperature molten steel and air and prevent secondary oxidation of the molten steel.

[0023] (3) The end point components of the alloy configuration need to be added during the steelmaking process of the converter. By increasing the temperature of the alloy added to the converter, the temperature drop effect on the molten steel can be reduced, thereby reducing the temperature loss of the molten steel.

[0024] (4) The steel-making process requires a ladle to contain and transfer the molten steel, and the casting process requires a tundish to transfer the molten steel. Increasing the online temperature of the ladle and tundish can reduce the steel-making temperature of the first two furnaces before the ladle and tundish are put into use by more than 1°C.

[0025] The beneficial effects of adopting the above technical solution are:

[0026] The present invention adopts a series of measures to reduce the temperature drop in the process during the steel-making process, the argon blowing process, the ladle insulation and other related links, so that the average steel-making temperature of the steel plant is reduced by more than 10°C, the alloy recovery rate of the converter is steadily improved, the quality of molten steel is improved, the consumption of refractory materials and industrial gases is reduced, and the low-temperature balanced controllable converter steelmaking system is achieved. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In order to achieve the goal of reducing the steel-out temperature of the converter, the applicant of the present invention has made the following improvements to its No. 2 converter:

[0029] 1. Add an alloy baking device behind the furnace. The alloy baking device is planned to adopt converter gas + oxygen-enriched mode to centrally bake and heat each furnace of alloy materials, further reduce the temperature drop during the steel-out process, and achieve a baking time of ≥5 minutes per furnace, and an alloy baking temperature of ≥300°C (the baking temperature rises gradually with time, and can reach above 500°C in 15 minutes). If the average baking temperature of each furnace alloy reaches 300°C, the steel-out temperature can be reduced by 5°C.

[0030] The baking of converter alloys is limited by the small particle size of No. 75 silicon carbide in the existing alloy. The high alloy baking temperature and long baking time can easily cause alloy agglomeration, resulting in blockage in the alloy baking bin. Therefore, the high fire time of the alloy baking is currently controlled. After a single alloy is added, the alloy baking high fire time will automatically turn to low fire after 6 minutes.

[0031] The theoretical benefit of reducing the tapping temperature by heating the alloy is calculated as follows:

[0032] (1) Assuming the average baking temperature of each furnace alloy reaches 300℃, the tapping temperature can be reduced by 5℃, and the annual output of 1.4 million tons of steel billets can be reduced by 0.6 yuan / ℃. The production cycle of each furnace of the converter is 25 minutes, and the baking time of each furnace alloy is ≥5 minutes. The benefit of reducing the tapping temperature = 140×5×0.6 = 4.2 million yuan / year;

[0033] (2) Energy operating cost of a single furnace

[0034] The average converter gas flow rate is 600Nm 3 / h, average oxygen consumption 65Nm 3 / h, converter gas price 0.12 yuan / Nm 3 , oxygen is 0.5 yuan / Nm 3 , calculated based on an annual output of 1.4 million t / a of steel billets from a single furnace.

[0035] A. Annual maximum consumption cost of converter gas: 600Nm3 / h×25 / 60h×0.12 yuan / Nm3÷80t×1.4 million t / year≈525,000 yuan / year;

[0036] B. Annual maximum oxygen consumption cost: 65Nm3 / h×25 / 60h×0.5 yuan / Nm3÷80t×1.4 million tons / year≈237,000 yuan / year;

[0037] C. Annual power consumption of fans: 7.5kW×25 / 60h×0.54 yuan / kWh÷80t×1.4 million tons / year≈30,000 yuan / year;

[0038] (3) Comprehensive economic benefits = 420-525-237-3 = 3.408 million yuan / year.

[0039] 2. The existing ladle casting is naked casting, and the high-temperature molten steel directly contacts the air to inhale, which greatly increases the oxygen, hydrogen and nitrogen in the molten steel. At the same time, the steel flow forms slag rolls in the steel landing area, and the insufficient floating into the crystallizer is easy to form large-particle inclusions in the ingot. According to relevant research and peer benchmarking, the use of long shroud protection casting can reduce the total oxygen content in the steel by 10-20ppm and the nitrogen content by 5-10ppm, effectively reducing the large-particle inclusions in the molten steel, and can effectively ensure the quality of large-size and low-compression steel bars. At the same time, due to the exposed radiation heat dissipation of the molten steel, according to the statistical analysis of our company's big data, it is as high as nearly 5°C. Through the long shroud protection casting of the ladle, matching the ladle manipulator bowl seal and nitrogen seal, the high-temperature molten steel is prevented from contacting with the air, while improving the purity of the ingot, reducing the temperature drop from the ladle to the middle ladle, thereby providing the necessary basic conditions for reducing the tapping temperature of the converter.

[0040] 3. The ladle baking device originally used converter gas for baking, the ladle online temperature was only 750-800℃, the tundish online temperature was only 500-600℃, the baking fire was manually adjusted by manual valve mode, there was no PLC control system, the ladle could not be baked according to the refractory temperature rise curve, and many safety indicators did not meet the requirements of the specifications. The ladle baking device was modified according to the following requirements.

[0041] (1) The ladle must be baked with blast furnace gas + oxygen-enriched gas, the flame length must be greater than 3 meters, and the flame must be able to reach the bottom of the ladle directly;

[0042] (2) It is possible to use blast furnace gas + oxygen-enriched gas and converter gas as the main baking gas source; natural gas is used as a backup gas source to meet the baking temperature requirements;

[0043] (3) Newly built ladle, magnesia carbon brick refractory, blast furnace gas + oxygen enrichment, baking time ≤ 48 hours, final baking temperature ≥ 1000°C;

[0044] (4) For small and medium repair kits, the baking time is ≤15-25 hours, and the final baking temperature is ≥1000℃;

[0045] (5) Comply with the Steelmaking Safety Regulations, safety interlocks and related safety standards.

[0046] The specific transformation measures are as follows:

[0047] (1) The diameter of the converter gas pipeline in the plant connected to the roaster pipeline was changed from the original DN125 to DN200mm;

[0048] (2) Before the converter gas pipeline in the plant is connected to the manual gate valve of the blast furnace gas pipeline (DN200);

[0049] (3) The original DN500 blast furnace gas pipeline outside the factory building was replaced with DN800 to ensure the supply of blast furnace gas for subsequent baking units;

[0050] (4) A branch oxygen pipeline is laid at the end of the 1-6 position roaster, and a nitrogen purge interface for the instrument is reserved;

[0051] (5) The natural gas pipeline is changed to DN80mm pipe diameter and the matching valve is connected to the burner;

[0052] (6) The burner can realize blast furnace gas + oxygen-enriched; converter gas + oxygen-enriched; natural gas + oxygen-enriched, three different energy media can be effectively switched;

[0053] (7) The oxygen-enriched air with an oxygen-enriched concentration of 21% is oxygen-enriched air, with branch oxygen added to the primary air duct of the burner and cyclone blades added to the secondary air duct. Oxygen enrichment improves the complete combustion of coal gas, and cyclone blades enhance the premixing of air and gas.

[0054] (8) A preheating box is set on the cover, and the combustion air is heated by the heat storage body and then divided into two paths and then collected to the burner, thereby improving the thermal efficiency of baking.

[0055] The index data of 6# roaster before and after the transformation are as follows:

[0056] Before transformation: Gas medium used: converter gas, average hourly consumption 800m 3 / h, the end point temperature of the ladle on line is 750-800℃;

[0057] After transformation: The fuel medium used was blast furnace gas + oxygen, which was later switched to converter gas. The average hourly consumption of blast furnace gas was 949.14 m 3 / h, average oxygen consumption per hour 67.28m 3 / h, the average hourly consumption of converter gas is 724.88m 3 / h, the end point temperature of the ladle on line is 1000℃ (one month’s on-site tracking data).

[0058] 4. The method of steel tapping from the converter adopts the method of direct steel tapping from the converter without turning over the converter: after the oxygen lance is lifted at the end of the converter blowing, the oxygen lance is automatically lifted to the waiting position, the oxygen lance control mode is switched, and the manual control of the lance position is realized. The oxygen lance head is inserted into the furnace mouth by 1.0-1.5m through manual control. According to the difference between the absolute height of the oxygen lance and the absolute height of the furnace mouth, the depth of the oxygen lance head entering the furnace mouth is judged. Open the nitrogen shut-off valve, open the flow regulating valve to 100%, and continue to blow nitrogen for 10-30s to blow away the slag layer in the furnace. The nitrogen blowing time is determined according to the slag splashing out of the furnace mouth. After the nitrogen blowing starts, if a large number of dense slag pieces appear at the furnace mouth, the blowing time is controlled according to the upper limit of 30s; if only a small amount of slag pieces splash out of the furnace mouth, the blowing time is controlled according to the lower limit of 10s.

[0059] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for reducing the tapping temperature of a converter, characterized in that: The steps include: (1) The converter steel-tapping method adopts the converter steel-tapping method without turning over the converter: after the oxygen lance is lifted at the end of converter blowing, the depth of the oxygen lance tip entering the furnace mouth is determined according to the difference between the absolute height of the oxygen lance and the absolute height of the furnace mouth, the oxygen lance tip is inserted into the furnace mouth, the nitrogen shut-off valve is opened, and nitrogen is continuously blown. The nitrogen blowing time is determined according to the slag splashing out of the furnace mouth; (2) In the continuous casting process, long shroud and argon blowing protection casting are used for ladle casting; (3) Control the temperature of the alloy added during the converter steelmaking process to be ≥300°C; (4) The ladle is baked according to the refractory temperature rise curve, the baking time is ≤15-25h, and the ladle end temperature is controlled to be ≥1000℃.

2. The method for reducing the steel tapping temperature of a converter according to claim 1, characterized in that: In the step (1), the oxygen lance tip enters the furnace mouth at a depth of 1 to 1.5 m.

3. The method for reducing the steel tapping temperature of a converter according to claim 1, characterized in that: The nitrogen blowing time in step (1) is 10-30s.

4. The method for reducing the steel tapping temperature of a converter according to claim 1, characterized in that: In the step (2), the argon blowing flow rate of the long shroud is controlled to be above 55 L / min.

5. The method for reducing the temperature of steel tapping in a converter according to claim 1, characterized in that: In the step (3), an alloy baking device is used to bake and heat the alloy. The fuel gas medium used by the alloy baking device is converter gas, and the combustion mode is oxygen-enriched combustion.

6. The method for reducing the tapping temperature of a converter according to claim 1, characterized in that: In the step (4), the ladle baking is carried out by using a ladle baking machine, and the fuel gas medium used by the ladle baking machine is blast furnace gas, oxygen and converter gas.

7. A method for reducing the temperature of steel tapping in a converter according to claim 6, characterized in that: The diameter of the pipeline connecting the converter gas to the gas inlet of the ladle roaster is 200 mm, and the diameter of the pipeline connecting the blast furnace gas to the gas inlet of the ladle roaster is 800 mm.

8. The method for reducing the steel tapping temperature of a converter according to claim 6, characterized in that: The ladle cover of the ladle roaster is provided with a preheating box.